Deflection circuits for cathode ray tubes



July 20, 1955 R. R. HOFFMANN DEFLECTION CIRCUITS FOR CATHODE RAY TUBES 2Sheets-Sheet l Original Filed March 2, 1959 .Illlll IN V EN TOR.

BY RICHARD R. HOFFMAN und July 20, 19.65 R. R. HOFFMANN DEFLECTIONCIRCUITS FOR CATHODE RAY TUBES Original Filed March 2,

2 Sheets-Sheet 2 AA V ORN

Utlitd 81131168 Patent O ce arsenic nnnrnerrort cincnrrs non baritonerunas The present invention is directed generally to sweeping spectrumanalyzers and in particular to sweep control circuits.

This application is a division of copending application Serial No.796,687, tiled March 2, 1959, now Patent No. 3,017,573.

lt is desirable, in frequency scanning or frequency modulating devices,to be able to vary the width of the band of frequencies which is scannedby the device while laintaining constant its center frequency. lngeneral frequency scanning in such devices is accomplished in responseto a periodical varying signal the magnitude of the variationdetermining the scanned band width, while the center frequency of thefrequency band under examination is controlled in response to a DC.variable voltage. ln one aspect of the present invention, there isprovided a novel mixer circuit for combining the varying sweep widthcontrol voltage and the DC. center tr quency control voltage, eachwithout interaction on the other. The invention finds particular utilityin frequency scanning devices having a low scanning rate, and where thecenter frequency of the scan is required to remain lixed while theextent of scanning is being varied.

Since such scanning devices are commonly employed in frequency scanningpanoramic receivers, also known as spectrum analyzers, the inventionwill be described as applied to such a device, without intending tolimit the scope of the claims to any particular application.

Panoramic devices are employed to display visually the frequency contentof a band of frequencies, i.e. the amplitude of each signal within theband plotted against a base line effectively calibrated in terms offrequency. t frequency scanning receiver' is employed, in the morecommon types of panoramic devices, which scans over a frequency bandunder examination in response to a periodic scanning voltage waveapplied to a voltage responsive tuner of frequency scanning device,included in the frequency scanning receiver. The extent of width ot theband of frequencies which is scanned by the device is then a function ofthe peak-to-peak magnitude of the periodic scanning voltage, and meansare provided for controlling and varying this magnitude in order toenable scan width control. The center frequency or the frequency bandunder examination is also subject to control, by applying a controllableDC. voltage to the voltage responsive tuner or scanning device.

ln order to provide a visual display oi the frequency content of theband of frequencies, a cathode ray tube indicator is commonly employed.ln such cases the ray ot the indicator is usually swept in onecoordinate direction in synchronism with the scanning voltage, toprovide a base line calibratable in frequency, and is deilccte inanother coordinate direction in response to the signal output of thefrequency scanning voltages. A plot of amplitude against frequency isthus generated on the face of the cathode ray tube.

ln a preferred form of the invention, frequency scanning of theoscillator of a superheterodyne receiver is accomplished by varying acontrol voltage applied to a electronic control circuit. The controlvoltage is preterably of sawtooth form, and is coupled to the electroniccontrol circuit by a cathode follower circuit. The sweepwidth of thescanned frequency spectrum is then determined by the maximum amplitudeof the sawtooth scanning voltage, which may be varied by a voltagedivider. ln addition to the sweepwidth control circuit, there isprovided a center frequency control circuit, for determining the centerfrequency of the frequency band through which the local oscillator isswept. The center frequency control circuit provides a DC. voltage,which is applied to the reactance tube to determine its xed biasvoltage.

One feature of this invention is the provision of a mixinfy circuit forcombining the center frequency and sweepvidth control voltages, theoutput of the mixing circuit being connected to a single control elementof the electronic control circuit Miller tube or reactance tube, tocontrol both the fined voltage and the voltage variation appliedthereto.

A problem arises in the use of spectrum analyzers in the low frequencyportion of the spectrum say from 0 to lC-,OGG cycles where it is oftennecessary to resolve two signals which may be separated by only 2cycles.

l esolution is a function of both sweep width and sweep rate. lngeneral, if sweep width is increased, sweep rate in st be decreased tomaintain the same resolution. l-lowever, operationally it is desirableto employ a fast can rate when a wide portion of the spectrum is beingsearched. Accordingly there is provided means for automaticallyincreasing the scanning or sweep rate as the sweep width is increasedand simultaneously automatically adjust the bandwidth of filter circuitsto provide optimum resolution for any resulting combination of sweepwidth and sweep rate.

A further feature of this invention is the provision of to permitvarying of the sweep rate While maintaining constant a given resolution.

The present invention provides a sawtooth sweep generator circuitemploying a series circuit comprising a AC. voltage source, a resistorand a capacitor. The capacitor charges at an exponential rate and byemploying a long time constant the charging curve is made quite linearin the beginning. A vacuum tube in parallel with the capacitor isemployed as a switch to control the charge and discharge points of thecapacitor. The discharge taking place through the vacuum tube. A novelcircuit controls the operation of the switch tube so as to independentlydetermine the charge and discharge points. rthis permits the independentdetermination of the lett and right edges of the display on a cathoderay tube employing the sawtooth sweep as a time base generator. Furtherit permits selection of a portion of the charging curve of a desiredlinearity or non-linearity, if say an exponential sweep is desired.

These and still other features and advantages of the invention will bepointed out with particularity or will become obvious as the followingdescription proceeds taken in conjunction with the accompanyingdrawings.

ln the drawings:

FGURE l is a schematic diagram of a spectrum analyzer.

FGURE 2 is a detailed circuit diagram ot a portion of the apparatusshown in FIGURE l.

in FGURE l there is shown the torni of a block diagram a spectrumanalyzer employing the instant invention.

The signal to be analyzed is fed to an input amplifier Ztl which may bearranged to amplify or attenuate the incoming signal to a desired level.The signal is then applied, usually through a cathode follower, to abalanced mixer stage Z2. An oscillator signal from oscillator 2li islikewise applied to the mixer 22. The outalessio put of the mixer is fedto a conventional plate tank circuit, tuned to a desire-d intermediatefrequency. Thus, only sidebands lwhich approximate the intermediatefrequency will appear at the output of the balanced mixer 22.

A crystal filter stage 26 is used to lter the signal to permit only aband of a given bandwidth to pass to intermediate ampliiier 28.

The crystal filter is of a type permitting variation in the pass bandwidth by varying of a control 3d (shown schematically).

A conventional means for varying the bandwidth is to employ a variableresistance, as control 3?, in parallel with a tuned plate tank circuitand which acts in series with a crystal to vary the bandwidth of thecrystal filter. Such crystal filter circuits and methods of varyingbandwidth are wel known to the art.

It is also conventional to employ a number of crystal filters in cascadeto obtain the desired bandwidth.

It is necessary to maintain a particular relationship between bandwidth,sweep width, and sweep rate to maintain optimum resolution.

The signal of the desired frequency spectrum is then amplified byamplifier 2S and the -signal detected in detector 32. The output of the'etector is amplified in vertical deflection amplifier 3d and applied tothe vertical deflection paltes 36a and Sb of cathode ray tube 38. Gtherdisplay means such as recording devices, may be substituted for thecathode ray tube.

The oscillator 24 is electronically controlled by electronic controlcircuit 40. The oscillator may be, by way of example, of the Hartleytype and the electronic control circuit may be a Miller Tube orreactance tube circuit.

A sweep generator 42 provides .a sweep signal to the Ihorizontalamplifier t3-s which is amplified iand `applied to plates de of cathoderay tube 33.

The sweep generator also provides a signal to the electronic controlcircuit d@ to control the center frequency of the oscillator a-s well asthe sweep range.

The foregoing description is typical of prior art spectrum analyzers.

The present invention diff-ers in the unique features of the sweepgenerator which will be described hereinafter in greater detail.

In this circuit, a capacitor S is charged from a high potential sourceshown as a 1200 volt DC. source through a resistance 52. The timeconstant is chosen to provide a long charging time relative to the sweeptime of the horizontal sweep. For example by using a lafd. capacitor anda 1.5 megohm resistor 52 a time constant of 375 seconds is obtained. Byemploying a second maximum sweep time, the circuit utilizes an extremelylinear portion of the voltage curve as measured across the capacitor.

In the present embodiment, the design permits electronic control of aDC. coupled saw-tooth generator whose period can be adjusted from l to30 seconds.

Discharge of capacitor 5d is controlled by a switch which in thisinstance is a vacuum tube 5d. The switch tube 54 is controlled bymultivibrator 56. As will be discussed in detail hereinafter withreference to FTG- URE 2 the capacitor voltage, appearing on the grid o-fa cathode follower yamplifier which is cascaded to amplifier 62 and inturn drives paraphase differential arnplitier stage 4d. The dual outputof amplifier 44 is directly coupled to horizontal oscilloscopedetiection plates 46. The output of the paraphase amplifier de is alsoapplied to -a pair of individual variable voltage dividers 61 and 63connected to a negative source of voltage. The voltage dividers drivethe grids of a dual triode cathode follower amplifier (not shown in thesimplified showing of FlGURE l) whose output provides positive controlof the multivibrator.

One plate of this multivibrator operates the capacitor shorting switchtube 54 to complete the loop. Although the capacitors charge attempts toreach the full 1200 volts, it never reaches this because the circuit isdesigned to limit the voltage build-up to well within the linear portionof the logarithmic charge rate curve. That is, the liip-iiop circuit 56causes the capacitor 50 to discharge after a maximum of 30 seconds ofthe 375 total RC time constants. lf, for example, a l() second sweep isdesired, the output of amplifier i4 is maximized so that the .paraphaseamplier output quickly reaches the level required to reverse themultivibrator.

in addition to driving the local loop, a second output from thecapacitor-amplilier, after further application by amplifier 60 controlsthe electronic control circuit liti, as for example the grid of .aMiller tube which in turn controls a Hartley oscillator. The signalfrequency may be divided as by Eccles-.ordan division and theintermediate frequency signal fed to a balanced modulator, alsoreceiving a 0 to 5 kc. input. The latter is from the circuit underspectrum analysis. One of the mixers output side bands passes throughamplifying and crystal filter circuits 26 to a diode detector 32. Theresulting envelope is applied to the vertical deflection plate of theoscilloscope. In this way, the spectrum of the test circuit is frequencyswept once with each horizontal sweep of the scope. Gangedpotentiometers 7G, 72, and 3@ simultaneously adjust the sweep rate andthe sweep width for best search condition and automatically varies thebandwidth of the crystal lilter to maintain optimum resolution for theparticular sweep rate and sweep width. Thus, the operator may controlhis analysis incrementally from `full time to a minimum time. Thisallows him to select portions of the frequency sweep which interest himmost, reducing the overall time for the analysis. By gauging the sweeprate and sweep width control and filter band width, no calculations areneeded to obtain optimum resolution for any particular sweep rate andsweep width. A conventional regulated power supply energizes theapparatus.

Referring now to the schematic circuit of FIGURE 2 showing in detail thesweep generator circuit ft2. Tube Sd acts as an on-off switch to controlthe discharge of capacitor Eil. Tube 54 is connected in parallel withcapacitor 50 to the grid of cathode follower amplifier 80. When switchtube 54 is non-conducting, capacitor 5t? tends to charge up to 1200volts through resistor 52 (time censtant 375 seconds). Basically, thevoltage appearing across cathode follower resistor 82 drives grid oftube employing cathode resistor 86 across which an output signal isderived and fed to two circuits. One circuit includes dual amplifier 88employing a cathode follower circuit which controls the voltage appliedto the electronic control circuit 40, such as the grid of a Miller tube.This output is derived across cathode follower resistor 92. .in turncircuit 40 controls the frequency swing of say a 200 to 300 kc. Hartleytype oscillator 24. The potential derived across cathode followerresistor 36 is applied to potentiometer 9d, which acts :as a voltagedivider serving as a sweep width multiplier, to the grid of tube 44a.Dual tube dd serves as a paraphase amplifier whose cathode resistor lil@provides an output voltage to `a jack 193 providing means for couplingto an external display means. Tube sections 44a and 1Mb produce voltages180 degrees out of phase with each other. A positive voltage on the gridof tube section 44a causes a negative signal to appear on the plate ofthat tube section and a positive signal on the plate of tube section Mb.These voltages are applied directly to the cathode ray tube horizontaldeliection plates lea and leb and to individual voltage dividerpotentiometers 6l and 63. These voltage dividers are connected to anominal volts source, yand potentiometer taps, slightly positive, drivethe grids of dual tube ltl. The decoupling cathode follower circuit oftube 10ft controls the state of flip-flop multivibrator 56. Positivelydriven to each state, the multivibrator timing is determined by settingof the wipers or" potentiometers 61 and 63. When the plate 56a of tubeSe goes negative, tube 54 cuts oil, and capacitor Sti charge When thestate is reversed, tube d conducts discharging capacitor Sil producing anearly vertical trace ily-back voltage. This voltage pulse, amplifiedand passed around the loop again, reverses the llip-llop S6 back to itsorigin-al state, repeating the cycle. Maximum and minimum voltageexcursions of capacitor are determined by potentiometers el and 63respectively. Resistor lilo and neon lamp ltlt shunting capacitor 5@limit the charge on capacitor 5d. The cathode potential ot tube 54 isbrought to a negative potential (-160 volts) to permit completedischarge of capacitor Sil if desired. Cathode resistor 32 of tube 8l)is shunted by a voltage divider comprising resistors lll, 112, 113, and7d. Resistor M3 is a DE. balance control establishing identical voltageat resistor i12 and the cathode of tube 8?. balances out any DC.voltages .appearing in the output. Resistor lll and resistor ll?,establish maximum and minimum sweep duration. Resistor 70 may beemployed as a front panel control accessible to the operator to providein a typical installation from three to thirty seconds sweep ratevariation. It is to be understood other time ranges may be employed ifdesired. Variable potentiometer resistor 72 (with maximum and minimumcontrol variable resistors ld?. and 14d) acts as a voltage divider forthe output from the cathode follower of tube dei. These resistors serveas the sweep width control circuits which drive the electronic controlcircuit ln one embodiment a sweep range determinable by a Miller tube offrom 6G to 600 cycles was provided.

Potentiometer 9d, which could be a step type variable resistor, servesas a sweep width multiplier. When the wiper is set at maximum, the fulloutput from tube appears at the grid of amplilier 44a. lf the wiper isset, say, at the electrical center of the potentiometer, only half theoutput of tube 554i will appear on the grid of tube Assume now that thecircuit constants are such that with the wiper of potentiometer M- is inthe maximum position and the charge on capacitor 5d reaches 19t) volts.Then the multivibrator 56 will cause tube 5d to conduct. lt will be seenthat if the wiper of potentiometer 9d adjusted so as to apply half theoutput voltage from tube 8d then it will be necessary for the capacitorto charge to 2G@ volts in order to provide a sufficient voltage at thegrid of tube ido to cause tube 5d to be rendered conductive. Since thecharging rate of the capacitor is constant, the eiect of controlpotentiometer 9d is to provide means for changing the length or durationot the sweep. It is a particularly advantageous feature of thisinvention that for all settings of potentiometer 9d, as the sweep timeis changed the sweep width is also changed, so as to maintain constantthe resolution but presenting on the display, more frequently, a smallerportion of the spectrum.

The sweep width is initially determined by the setting of control 72which is ganged to sweep rate control 7@ and bandwidth control 30. Thevoltage signal from control 72 is applied to the grid of tube 83a.Associated with amplilier 8de there is provided a cathode resistor 1145in the circuit of tube 88a. The center frequency of sweep oscillator isdetermined by the voltages applied to the grid of tube @3b. The voltageto tube @Sb is derived crom a voltage divider comprising resistors 149,15d, and 315i. Resistor ltl is a variable resistance and provides a zerofrequency adjust means while resistor ll is a potentiometer. The wiperof which is connected to isolation resistors 146 and ldd. The grid oftube 33.5 is connected to a common junction of resistors 14:6 and 14S.The output of tube dub is derived across cathode resistor K11 and isapplied to the electronic control circuit which as indicated may be aMiller tube. Gas tube lett serves as a voltage stabilizer for the DC.voltage applied to the grid of tube tlib.

When in the closed position switch lol provides for recurrent operationof the sweep. When switch ll is in open position, then switch la?) maybe closed to manually trigger the circuit. The diodes, resistors andcapacitors shown associated with tube 56 are part of a conventionalmultivibrator circuit.

rthe operation of this invention will now be described in conjunctionwith a spectrum analyzer designed to operate in the zero to livelrilocycle spectrum range with a sweeping oscillator adapted to cover a2O cycle to 690 cycle portion or the spectrum. As the signals are tun-edin, they appear as vertical pips on the horizontal axis or" the cathoderay tube. Their location, relative to a reference point, along thehorizontal axis will indicate irequency, and the height of the pip willindicate amplitude. Change of center frequency and sweep deviation areobtained by means of calibrated tuning controls.

As the visual sweep width of a convention-al prior art spectrum analyzeris increased, or decreased, the resolution on the screen of the receiverrespectively becomes narrower or wider. Generally a wide band spectrumanalyzer has less frequency resolution than a narrow band analyzer, andwhile the irst one permits a more rapid survey of wide regions of thefrequency spectrum, the second one permits more accurate survey when thesignals are quite close to each other.

The optimum -esolution obtainable between adjacent signals is a functionof filter bandwidth, sweep-rate, and sweep width. These are designformulas known to the art for determining the relationship between thepmameters to provide optimum resolution. Assuming now that therelationship between potentiometer controls 7d, 72, and 3d afectin-grespectively the sweep-rate, sweep width and bandwidth of crystal titer2d are so chose l Lhat as the sweep width control is varied, the optimumresolution frequency will vary so that at a very small sweep width ofsay 2t) cycles which corresponds to ilO cycle and a sweep rate of l0seconds. A line resolution of 2 cycles is obtained. At this narrowbandwidth the fine resolution is an operational requirement. On theother hand, at a 200 cycle sweep width a resolution in the order of 22cycles is adequate.

As the sweep width is increased to 29() cycles, the sweep rate ymay 'beincreased to 1 second as a resolution of 22 cycles is adequate. The bandwidth must also be adjusted to maintain optimum resolution for thechosen swelep rate and sweep width in accordance with the formu a:

Where B is the desired bandwidth in cycles, SW is the sweep width incycles, `and SR is the sweep rate in cycles/ second It is to be notedthat as the sweep width is increased the sweep rate is also increasedsince the resolution requirement is not as stringent at wide spectrumwidths.

ln operation, the operator searches for a signal by sweeping across thefrequency spectrum to be studied using the wides-t sweep width availableon the instrument. Upon detectinU the presence of a signal, he then. redthe sweep width so as to be able to separate and analyze adjacentsignals. As the operator varies control 7,2 to reduce the sweep width,he simultaneously varies contr l 7d, which is ganged to control '72,thereby decreasing the sweep rate. rthe band width control is likewisesimultaneously varied so as to reduce the bandwidth to maintain optimumresolution for the particular values of sweep rate and sweep width. Theoperator having detected the signal and resolved it now desires tomonitor the particular signal. However, in low frequency spectrumanalysis the sweep times become extremely long and exceed the storagetime of cathode ray tubes of normal persistence unless special storagetype tubes are employcd. Therefore, it is desirable to maintain the sameresolution at a higher sweep rate. Resolution in cycles may beapproximately determined 'by the formula:

n=(1.3i0.3)\/1.s(SW)(SR) (2) Where R is resolution in cycles, SW issweep width in cycles, and SR is sweep rate in cycles/ second Referenceto the formula will show that the resolution may be maintained if the.sweep width is decreased and the sweep rate is increased in inverseratio. It is to be noted that the mechanical gauging of controls '70,72, and 3@ does not maintain a fixed resolution and that if the sweeprate is increased the sweep width increases contrary to the requirementsof `Equation. 2 for maintaining Xed resolution.

As the operator varies control 94, he increases the sweep rate anddecreases the sweep width, thus, displaying a smaller portion of thespectrum in a shorter period of time while maintaining the sameresolution. Another advantage of t-his shorter time period is thatrepeated displays of the signal under study is frequently madepermitting the operator to detect non-repetitive or short durationsignals.

Controls 61 and 63 permit the adjustment of the left and right edges ofthis display with respect to the center of the tubes independently ofeach other. An important advantage of this circuit is that by varyingcontrol 61 and 63, a linear portion of the charge curve of capacitor Silmay be selected.

Another important advantage of the disclosed circuit is that withchanges in horizontal detlection the left and right edges of the displaycan be controlled independently. In a spectrum analyzer there isnormally employed a calibrated screen in front of the tube face tolpermit the operator to directly interpret the frequency being observed.`lf tube aging occurs or other drifting of component values arise duringuse, `the line .size must be readjusted so as to match the calibrationson the screen. However, the apparatus of the present invention is notsubi-ect to this disadvantage since the left and right edges of thepicture are determined by the operational voltages derived from thecontrols 61 and 63 and, therefore, the deflection voltage is not aiectedby minor change in component values.

The center frequency determining D.C. potential is independent of theA.C. signal derived from the cathode of tube 88a. 1t will be noted thatthe cathode resistors of tubes 80, S4, and 88 are returned to a -100Volts bus. D.C. balance control 113 provides means to balance out theD.C. potential with respect to ground.

Having thus disclosed the invention, what is `claimed is:

li. in combination with a cathode ray tube having electron beamdeflection means:

(a) a source of D C. potential;

(b) a two-electrode capacitor having one electrode connected to aportion of said source of DC. potential of one polarity;

(c) a resistor connected between the other said electrode of saidcapacitor and a portion of said source of DC. potential of a secondpolarity;

(d) a vacuum tube having its plate-cathode circuit connected in parallelwith said capacitor;

(e) on-oi control means connected to said vacuum tube to control itsplate-to-cathode conduction so as to control the discharge of the saidcapacitor;

(f) a paraphrase amplier arranged to provide a pair of related outputvoltages to output means connected to the electron beam deflectionmeans; and

(g) variable means for applying a selected portion of one of said outputvoltages to said on-otf control means to place said control means in anon position when one of said related output voltages is of a firstpotential level and a variable means for applying a selected portion ofthe other of said related output voltages to said on-ott control meansto place said control means in an oli position when said output is at asecond potential level.

2. A controlled RC. charging network, including a source of D C.potential, a resistor connected to said source and a capacitor connectedacross said resistor and said source for charging said capacitor fromsaid source through said resistor, and means to control the chargingcurve of said capacitor, said means comprising:

a vacuum tube having a control grid and a platecathode circuit inparallel with said capacitor;

a bistable means arranged to provide a blocking voltage to said gridwhenever the charge on said capacitor reaches a irst potential during adischarge cycle and to remove the blocking voltage so as to render saidvacuum tube conductive thereby discharging said capacitor whenever thecharge on said capacitor reaches a second potential during a chargecycle; and

means to independently adjust the response of said bistable means todesired values of first and second potential.

3. The apparatus of claim 2 wherein said bistable means is amultivibrator.

4. A controlled B C. charging network, including a source of DC.potential, a resistor connected to said source, and a capacitorconnected across said resistor and said source for charging saidcapacitor from source through said resistor, and means to control thecharging curve of said capacitor, said means comprising:

a Vacuum tube having a control grid and a plate-cathode circuit inparallel with said capacitor;

a bistable means arranged to provide a blocking voltage to said gridwhenever the charge on said capacitor reaches a first potential during adischarge cycle and to remove the blocking voltage so as to render saidvacuum tube conductive thereby discharging capacitor whenever the chargeon said capacitor reaches a second potential during a charge cycle; and

a pair of independently adjustable voltage sources, in-

terposed in cascade between said bistable means and said capacitor, saidsources being controlled by said capacitor charge so as -to provideoutput voltages proportional at all times to the charge on saidcapacitor, one of said voltage sources being adjusted to trigger thebistable means so as to render the said I vacuum tube nonconducting whensaid capacitor is discharged to a rst potential and until it charges toa second potential and the other of said voltage sources being adjustedto trigger the bistable means so as -to render said vacuum tubeconductive when said capacitor becomes charged to the second potentialand until it is discharged to the rst potential.

References Cited by the Examiner UNlTED STATES PATENTS 2,363,822 11/44Wendt 315-29 2,414,486 1/47 Rieke 315-29 X 2,428,926 10/ 47 Bliss 315-29X 2,467,834 4/49 Lasher 315-29 X 2,479,081 8/49 Poeh 315-29 2,508,8795/50 Zagor 315-29 X 2,519,030 8/50 Dome 328-156 2,620,441 12/52 McCoy etal 328-156 OTHER REFERENCES IRE Dictionary of Electronics Terms andSymbols, Institute of Radio Engineers, New York, 1961; p. 130,TK7804-15.

DAVID G. REDINBAUGH, Primary Examiner.

RALPH G. NILSON, Examiner.

1. IN COMBINATION WITH A CATHODE RAY TUBE HAVING ELECTRON BEAMDEFLECTION MEANS: (A) A SOURCE OF D.C. POTENTIAL; (B) A TWO-ELECTRODECAPACITOR HAVING ONE ELECTRODE CONNECTED TO A PORTION OF SAID SOURCE OFD.C. POTENTIAL OF ONE POLARITY; (C) A RESISTOR CONNECTED BETWEEN THEOTHER SAID ELECTRODE OF SAID CAPACITOR AND A PORTION OF SAID SOURCE OFD.C. POTENTIAL OF A SECOND POLARITY; (D) A VACUUM TUBE HAVING ITSPLATE-CATHODE CIRCUIT CONNECTED IN PARALLEL WITH SAID CAPACITOR; (E)ON-OFF CONTROL MEANS CONNECTED TO SAID VACUUM TUBE TO CONTROL ITSPLATE-TO-CATHODE CONDUCTION SO AS TO CONTROL THE DISCHARGE OF THE SAIDCAPACITOR; (F) A PARAPHRASE AMPLIFIER ARRANGED TO PROVIDE A PAIR OFRELATED OUTPUT VOLTAGES OT OUTPUT MEANS CONNECTED TO THE ELECTRON BEAMDEFLECTION MEANS; AND (G) VARIABLE MEANS FOR APPLYING A SELECTED PORTIONOF ONE OF SAID OUTPUT VOLTAGES TO SAID ON-OFF CONTROL MEANS TO PLACESAID CONTROL MEANS IN AN "ON" POSITION WHEN ONE OF SAID RELATED OUTPUTVOLTAGES IS OF A FIRST POTENTIAL LEVEL AND A VARIABLE MEANS FOR APPLYINGA SELECTED PORTION OF THE OTHER OF SAID RELATED OUTPUT VOLTAGES TO SAIDON-OFF CONTROL MEANS TO PLACE SAID CONTROL MEANS IN AN "OFF" POSITIONWHEN SAID OUTPUT IS AT A SECOND POTENTIAL LEVEL
 2. A CONTROLLED R.C.CHARGING NETWORK, INCLUDING A SOURCE OF D.C. POTENTAIL, A RESISTORCONNECTED TO SAID SOURCE AND A CAPACITOR CONNECTED ACROSS SAID RESISTORAND SAID SOURCE FOR CHARGING SAID CAPACITOR FROM SAID SOURCE THROUGHSAID RESISTOR, AND MEANS TO CONTROL THE CHARGING CURVE OF SAIDCAPACITOR, SAID MEANS COMPRISING: A VACUUM TUBE HAVING A CONTROL GRIDAND A PLATECATHODE CIRCUIT IN PARALLEL WITH SAID CAPACITOR; A BISTABLEMEANS ARRANGED TO PROVIDE A BLOCKING VOLTAGE TO SAID GRID WHENEVER THECHARGE ON SAID CAPACITOR REACHES A FIRST POTENTIAL DURING A DISCHARGECYCLE AND TO REMOVE THE BLOCKING VOLTAGE SO AS TO RENDER SAID VACUUMTUBE CONDUCTIVE THEREBY DISCHARGING SAID CAPACITOR WHENEVER THE CHARGEON SAID CAPACITOR REACHES A SECOND POTENTIAL DURING A CHARGE CYCLE; ANDMEANS TO INDEPENDENTLY ADJUST THE RESPONSE OF SAID BISTABLE MEANS TODESIRED VALUES OF FIRST AND SECOND POTENTIAL.